1. Field of the Invention
This invention relates generally to semiconductor switching devices, and more particularly to high current integrated switching devices.
2. Description of the Related Art
Many mixed-signal integrated circuit (IC) applications call for a device capable of switching high currents. One device which might be used for this purpose is a MOSFET. However, a MOSFET capable of handling the current to be switched is necessarily large, and may require an unacceptably large amount of area on an integrated circuit die.
Another device used for switching high currents is the silicon-controlled rectifier (SCR). One common SCR application is DC motor speed control, in which one or more SCRs are used to produce variable DC drive voltages from an AC line voltage. They are also used in lighting dimmer controls, and in phase control circuits used with inductive loads.
However, SCRs have a number of known shortcomings for integrated circuit applications. For example, parasitic capacitance within the device can cause it to be falsely triggered to turn on during fast voltage transients. For mixed-signal IC applications, on the other hand, the process design rules can make it difficult to form a reliable switch device which can be triggered at a desirable voltage level; in some cases, the triggering voltage may be too high for some circuit applications. Another limitation is that most SCRs require that the current passing from the anode to cathode terminal be reduced to near zero in order to be turned off. These drawbacks severely limit the types of applications in which a conventional SCR can be employed.